1. Field of the Invention
The present invention relates to a liquid-ejecting apparatus for ejecting droplets to an object, and to an ejection control device for controlling such an ejecting operation. Furthermore, the present invention relates to a method and a program for controlling such an ejection operation. Moreover, the present invention relates to a recording medium having the program recorded thereon.
2. Description of the Related Art
One of known techniques for gray-scale expression of a printing image is a pulse-number modulation technique. According to such a technique, each pixel, which is the smallest unit in an image, is expressed with a group of droplets having a small diameter. Depending on the number of droplets, the visual appearance of the diameter of each pixel changes. The visual differences in the pixel diameter give different gray-scale levels of pixels to a viewer. Here, the term “the number of droplets” refers to the number of droplets ejected to a pixel range of one pixel.
An application of such a pulse-number modulation technique is disclosed in WO01/039981 PCT Gazette. According to WO01/039981 PCT Gazette, droplets are ejected in a consecutive manner based on gray-scale data, i.e. data for determining the number of droplets to be ejected to one pixel range. For example, according to a gray-scale-level data item PNM5, five droplets are to be ejected in a consecutive manner. In detail, the gray-scale data and the pulse number are compared, and a signal that allows droplets to be ejected until the pulse number exceeds the number corresponding to the gray-scale data is generated.
However, such a technique that generates a driving signal based on the comparison result is problematic (first problem) in that it requires a complicated circuit for the ejecting position with respect to the center of the corresponding pixel.
Furthermore, WO01/039981 PCT Gazette and Japanese Unexamined Patent Application Publication No. 2003-226017, for example, disclose a line head functioning as a head mechanism in a liquid-ejecting apparatus. Such a line head has a plurality of nozzles aligned thereon and can draw pixels simultaneously with respect to the number of nozzles provided.
Such a line head is problematic (second problem) in view of the fact that an extremely a large number of nozzles are provided. For this reason, there are cases where some of the nozzles cannot eject droplets properly.